From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83A0BC282C8 for ; Mon, 28 Jan 2019 08:23:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 51FFD2148E for ; Mon, 28 Jan 2019 08:23:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548663799; bh=CDuTNVgfGfdfsdqHOILuN4/sQtGCbQMlhWeiJ9bCA/U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=YApXyK7xkthFOcogO0mmXkEUbnjcofW0vKt3Ea4XxWiJZxpZWItaCszl2kDFU0ddd Ix9Ej31DK7U6FswKdSOxNSXuvBAP4HWgsn2CV09Y9YSl0Phw1FdgsfpPENXFRK9LD3 9+uSofX2OJzmtfOrzCZ9fis+1+WNG+9a+cl1O46E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726790AbfA1IXR (ORCPT ); Mon, 28 Jan 2019 03:23:17 -0500 Received: from mail.kernel.org ([198.145.29.99]:59182 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726647AbfA1IXR (ORCPT ); Mon, 28 Jan 2019 03:23:17 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 255BE2148E; Mon, 28 Jan 2019 08:23:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548663796; bh=CDuTNVgfGfdfsdqHOILuN4/sQtGCbQMlhWeiJ9bCA/U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=h0pMFqEztXQdKYIYNX3xfcyJxwRTtcUSwU6OFakWm9aO7tH5kWSs3qa54h5lkEkdR BQ24ulB7FSK7q80PfLHI4bZLvOfIm+wocapkls39i6+EFs3p3YPMa18WKbiFDfHaPi 3zDwzl7TXHYHi+a3lYxn7jPxnZFXmR+UIEHIETj4= Date: Mon, 28 Jan 2019 09:23:13 +0100 From: Greg Kroah-Hartman To: Oleksij Rempel Cc: Linus Torvalds , Jiri Slaby , Pengutronix Kernel Team , lkml Subject: Re: [PATCH v1 3/3] drivers/tty: increase priority for tty_buffer_worker Message-ID: <20190128082313.GA15182@kroah.com> References: <20190110101232.9398-1-o.rempel@pengutronix.de> <20190110101232.9398-4-o.rempel@pengutronix.de> <20190110151953.qpat4t7lat6plfk6@pengutronix.de> <20190110163030.GB19693@kroah.com> <7a593f3b-0019-c30f-30e8-34eae7b96cf0@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7a593f3b-0019-c30f-30e8-34eae7b96cf0@pengutronix.de> User-Agent: Mutt/1.11.2 (2019-01-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 28, 2019 at 09:05:30AM +0100, Oleksij Rempel wrote: > > > On 10.01.19 17:30, Greg Kroah-Hartman wrote: > > On Thu, Jan 10, 2019 at 04:19:53PM +0100, Oleksij Rempel wrote: > > > > My gut feel is that if somebody still cares deeply about serial line > > > > latency, they should look at trying to see if they can do some of the > > > > work directly without the bounce to the workqueue. We use workqueues > > > > for a reason, but it's possible that some of it could be avoided at > > > > least in special cases... And yours sounds like a special case. > > > > > > It is for industrial low latency RS-422 based application. The loopback > > > test is just easy way to test/reproduce it without additional hardware. > > > > > > What is good, mainlineable way to implement it? > > > > What is the real problem your systems are having? Are they serial-port > > limited? Is latency a big issue? Trying to tune for a fake workload > > isn't the best way to solve anything :) > > The system in question is a high power laser cutter with live image-based inspection > and adjustment of the cutting process. In this setup the RS422 interface is used to > control parameters of the laser cutting unit in a tie control loop with the camera. > This loops needs to operate at 1000 Hz. > > The xy-stage moves with a speed of approx. 60m/min, i.e. within 1ms it > moves about 1mm. For a high precision control process a jitter of ± 500 us (+/- 0.5mm) > is unacceptable. Are you using the rt kernel patch for this type of thing? That should bound your jitter at a much more deterministic level. thanks, greg k-h